Room air diffusers and vents are well known. The simplest of these have no self-contained mechanism for regulating air volume whatsoever, but serve only as a final outlet for supply air to a room. Other types of diffusers include a control mechanism, but require electrical wiring, pneumatic piping or increased system pressure to power the mechanism, thereby limiting their application.
Some known diffusers include a self-contained, thermally-powered control mechanism. U.S. Pat. No. 4,231,513 (jointly invented by the inventor herein and Robert L. Vance, and assigned to Accutherm, Inc. of Novato, Calif.) is an example of such a device. That device utilizes a pair of thermostatic actuator elements, one sensing room air temperature and the other sensing supply air temperature, which are mechanically connected to and control the size of the diffuser opening. In the air cooling mode, the supply air element does not operate, and the size of the diffuser opening is controlled by the room air element only. In the air heating mode, however, the supply air element reacts to the warm air to result in a full open diffuser position. The room air element then reacts to the rise in room temperature by completely closing the diffuser (cutting off the warm air supply), or by first closing and then completely reopening the diffuser, which uncontrollably diverts more warm air into an already warm room.